A fastener is known from German Patent Application No. 199 24 502 A1. The known fastener includes a screw including a head and a shank. The head includes a supporting surface. The shank includes a cylindrical shank portion and a threaded portion including a thread. The cylindrical shank portion is located close to the head of the screw, and the threaded portion is located more or less close to the free end of the shank of the screw. The supporting element may be designed as a bush, a plain washer, and the like. The supporting element may also include a plurality of such elements. The supporting element includes a narrow location having a diameter which is smaller than the outer diameter of the threaded portion. The narrow location may be realized in a variety of different ways, for example by impressions being located on the circumference of the bush or by a continuous protrusion protruding towards the inside. It is also possible to arrange additional elements, for example a securing ring, in the inner diameter of the bush. When a plain washer forms the supporting element, the bore of the plain washer forms the narrow location in a way that it forms a continuous protrusion protruding towards the inside of the bush. The shank portion has a reduced diameter, meaning a diameter which is smaller than the outer diameter of the thread of the threaded portion. The reduced diameter of the shank portion may correspond to the rolling diameter of the screw during its manufacture.
When a thread is produced at the shank of the screw, especially by rolling, one automatically produces a thread runout facing the head of the screw. The diameter of the thread and of the threads, respectively, increases in the region of the thread runout facing the head of the screw. For example, the diameter increases from the rolling diameter to the outer diameter of the thread of the threaded portion being directly connected to the end of the thread. There are two different known standards for the thread runout: one is the “normal design” and the other one is the so called “short design”. In the normal design, the thread or the convolution extends about 2.5 rotations of the screw, meaning about 900°. In this portion, the outer diameter of the thread changes. The short design of the thread runout extends about 1.25 rotations, meaning 450°. Even shorter thread runouts are theoretically possible, but they cannot be produced in an economic way since the usable periods of time of the tools serving to roll the thread are comparatively short. No matter whether one uses the normal design or the short design, there is a theoretical (conical) enveloping cone in the region of thread runout of the thread of the screw. The supporting element with its narrow location may contact the enveloping cone. When one imagines the layout of the convolution of the thread of the threaded portion in a plane, there is a very long inclined plane having a comparatively small angle of inclination. The enveloping cone and this inclined plane of the thread runout, respectively, has the effect of the known supporting element getting clamped in the region of the thread runout.
Fasteners of this kind are especially used as dump elements at assembly stations. Usually, an automatic feeding station and a conveying station, respectively, is prearranged to the assembly station, the feeding station serving to place the fasteners in a position such that their axes are aligned, and such that the fasteners are located in a row. Such conveying apparatuses often use vibration drives. Due to the resulting vibrations, there is the danger of the supporting element getting fixedly connected to and engaging the screw such that the known fastener cannot be properly mounted in the assembly station. Even when the fasteners are separately fed to their place of application, there is the danger of the supporting element getting clamped in the region of the thread runout during transportation in a box, for example. These drawbacks do not only occur when the narrow location of the supporting elements is designed as local impressions being spaced apart the about the circumference of the supporting elements, but also when the narrow locations are designed to be continuous about the circumference of the supporting element. When choosing local impressions, there is the additional danger of these local impressions getting fixed by vibrations in the position in which they engage two adjacent convolutions of the thread in the region of the thread runout facing the head of the screw.
Another fastener including a screw and a supporting element being captively connected to the screw is known from U.S. Pat. No. 5,489,177. Especially, the supporting element is designed as a bush. In contrast to the fastener known from German Patent Application No. 199 24 502 A1 (which shows the production of the narrow locations at the bush being realized after having pushed the bush over the shank of the screw) U.S. Pat. No. 5,489,177 teaches to separately produce the screw, on the one hand, and the bush, on the other hand, and to afterwards connect the two elements. During the axial movement of the bush over the screw, the bush in the region of its narrow location is elastically expanded. After having passed a protrusion being located at the screw, the narrow location attains a comparatively small diameter. The screw includes a rolled protrusion being located between the thread of the screw and the cylindrical shank portion having a reduced diameter. The narrow location being located at the bush is produced at certain circumferential locations by axial displacement of material. The rolled protrusion at the screw has a conical surface allowing for pushing the narrow location of the bush beyond the protrusion of the screw. There is no danger of clamping of the narrow location at the outer diameter of the threaded portion—and also at the thread runout—since the narrow location and the threaded portion of the screw do not get in contact with one another.